1. Field of the Invention
The present invention relates in general to apparatus which are designed to move with precision over short distances or exert pressure against objects with a precise tactile force. More particularly, the present invention is directed to apparatus and the sensors which measure the movements and tactile grasp of robotic arms which form an integral part of such apparatus.
2. Description of Related Art
Apparatus such as robot assemblies are utilized in a number of different applications in which an arm is moved short distances or a hand grasps objects during the performance of a function. The effective performance of many of these apparatus depends upon the accurate determination of the distance moved by the arm or the tactile force exerted by the hand. Frequently movements on the order of one millimeter must be controlled so that demanding jobs can be completed with precision. Sensors which detect and determine movement distances and tactile pressures must be capable of continuously detecting the distances and sending the data to a feedback control system so that adjustments in the position of the robotics arm and movement can be made.
In robotics, many measurement and sensor systems have been developed to increase the performance and reliability of robots. Important properties to be measured include displacement, distance, motion, edge, force and tactile sense. One type of distance and displacement sensor known in the art is a magnetic position detector which is based on the Hall effect.
Magnetic position detectors measure small mechanical deflections by sensing variations in electromagnetic fields. One problem associated with the use of magnetic position detectors is their sensitivity to electromagnetic interferences. The information obtained from these magnetic position detectors becomes unreliable when they are subjected to electromagnetic fields which are not related to the robotic movement. Another problem with the magnetic position detectors is the requirement for electrical wiring and the associated electrical power. The use of these detectors in conjunction with measuring the position of robot arms presents potential explosion hazards when the robot is operated in an environment which contains flammable or explosive liquid or gas. In many instances, it is desirable to make these position measurements at high temperatures The robotics assemblies used in such high temperature situations must be both mechanically and thermally rugged. Unfortunately, robotics assemblies which use magnetic position detectors are not well suited for such high temperature applications.
Another type of sensor utilized in robotics is a fiber optic reflectance sensor. These sensors require two optical fibers referred to as a transmitting fiber and a receiving fiber as well as a means for reflecting the signal at the point of movement. In addition to requiring two optical fibers, reflectance response curves generated by these sensors are not linear. Furthermore, these sensors may be adversely affected by contamination of the optical surfaces which are exposed to ambient conditions.
In view of the above considerations, there presently is a need for robotics assemblies that are equipped with sensors which detect movements and tactile feel and are immune to electromagnetic interferences. There is also a need for robotics assemblies having sensors which avoid or minimize explosion hazards and are both mechanically and thermally rugged. The sensor should also be simple in construction without requiring additional components such as the means for reflecting signal mentioned above.